The diffusion of imipenem (IMP) in the knee joint was studied after a 1 g i.v. administration of Tienam over one hour. The synovial fluid was collected under anesthesia during arthroscopy carried out for mechanical lesions of the knee (meniscal lesions after ligamental injuries or sequelae after meniscectomy), in 3 groups of six patients at one, two, or three hours after the end of injection of IMP. The concentrations of IMP determined by high performance liquid chromatography (HPLC) were: 42.5, 20.1, 9.3 and 5.7 mg/l in the blood at T0, T1, T2 and T3 hr, respectively; 20.4, 13.0 and 7.9 mg/l in the synovial fluid at T1, T2 and T3, respectively. The decrease of IMP concentrations in the synovial fluid was 1,5 times as low as in serum. On account of its broad-spectrum antibacterial activity and our data, IMP could be used in perioperative prophylaxis of the knee joint surgery.